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Air bearing alternatives?

11-04-2012, 10:28 AM

I did not want to hijack the various tool grinder threads that are going on, so here goes:

I know the air bearing spindle is a bit of a reach for most of us, myself included, but I have some passive use of "ball bushings" for stuff at work in the past. (google it if you have not seen them...) They can be quite rigid and are very low friction with smooth movement. I have never priced them in larger sizes, so maybe there is no advantage in the end. I wonder if these could be somehow incorperated viable alternative or "middle ground" option that would be better than a standard spindexer, even if not quite up to air bearing standards.

I've seen a bunch of posts of successful endmill sharpening on a Quorn, which has common (non-precision) magneto bearings. Prof Chaddock's "trick" is to assembly the spindle, then machine it in-situ, which minimizes the runout. He strongly recommends that you don't ever disassemble the spindle, but that's more than sufficient for a home shop guy.

"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

Comment

The air bearing is for the workhead, not the grinding spindle. I think it is likely that even Prof Chaddock found it hard to sharpen small end mill flutes on his Quorn, which is a pity, because that is primarily what he designed it for. Some people have made their own air spindles but it isn't easy to do.

Comment

I did not want to hijack the various tool grinder threads that are going on, so here goes:

I know the air bearing spindle is a bit of a reach for most of us, myself included, but I have some passive use of "ball bushings" for stuff at work in the past. (google it if you have not seen them...) They can be quite rigid and are very low friction with smooth movement. I have never priced them in larger sizes, so maybe there is no advantage in the end. I wonder if these could be somehow incorperated viable alternative or "middle ground" option that would be better than a standard spindexer, even if not quite up to air bearing standards.

Any thoughts?

I had similar thoughts on using this type of bearing. You could use a piece of PGMS for the spindle and bore the support housing to suit the OD of the bearing. The main problem, as I see it, is to keep the grit out of the bearing, which the air bearing takes care of by virtue of the air entering the spindle bore in the middle and exiting at each end which should keep most grit out. I haven't done this, just thinking out loud!

Ian.

Comment

An air bearing spindle is not that hard to make. Philip Duclos wrote a series on making an endmill sharpener out of an import spin-indexer which he modified to make it air bearing. See HSM Sept.-Oct. '87and Nov.-Dec.'87. I made it and it works as advertised. It is used on a surface grinder but could easily be adapted to an ordinary tool and cutter grinder. The instructions for sharpening endmill flutes and lips are invaluable.

RWO

Comment

I had similar thoughts on using this type of bearing. You could use a piece of PGMS for the spindle and bore the support housing to suit the OD of the bearing. The main problem, as I see it, is to keep the grit out of the bearing, which the air bearing takes care of by virtue of the air entering the spindle bore in the middle and exiting at each end which should keep most grit out. I haven't done this, just thinking out loud!
Ian.

No reason that you could not pressurize any other type of workhead bearing housing with low pressure filtered air to exclude grit. I had some specialty wet grinders (used to grind glass, with typical ball bearings) that did exactly that to keep the grit and liquid out of the bearings.

Comment

An air bearing spindle is not that hard to make. Philip Duclos wrote a series on making an endmill sharpener out of an import spin-indexer which he modified to make it air bearing. See HSM Sept.-Oct. '87and Nov.-Dec.'87. I made it and it works as advertised. It is used on a surface grinder but could easily be adapted to an ordinary tool and cutter grinder. The instructions for sharpening endmill flutes and lips are invaluable.

RWO

Interesting, most accounts I have read of making air bearings seem to indicate that it can be a fairly demanding exercise. To be fair, I have not researched it all that much, so I may have a poor sense of what it takes. Would you care to elaborate a bit on what it takes, and how difficult it was? I've always sort of wanted one for my T&C grinder.

Not sure if Village press has back issues that far back, though I'm sure I could get reprints or it is likely to be found in one of the compilation books (Mr. Bulliss?). Sounds like it would be an interesting read.

Comment

The Phil Duclos air bearing writeup is in "The Shop Wisdom of Philip Duclos", available from Village Press.

Walter Meuller wrote several articles detailing improvements to the Quorn T&C grinder, including adapting the Duclos air bearing to it. These were several years ago, but might still be available as back orders. I don't have the issues available.

Jim H.

Comment

I built a machine once which had air-supported linear bearings. This was basically a sliding miter saw with a 16 inch blade and more than 5 ft of travel. The 'workhead' ran on parallel bars. The bearing blocks were made to float so they could self-align, then the adjusting bolts could be locked down. The workhead was well over 100 lbs, but with the blocks loose and aligned, it would quite easily float along the bars. I machined the blocks to suit the bars, and lined them with some thin uhmw, so with a 'touchdown' it was still possible to move the workhead along. What I found in the end was that when I secured the blocks mounting bolts, the friction increased slightly. There was no getting them perfectly aligned then keeping them that way while the bolts were tightened. It worked out well, but in future I'd use an epoxy to 'bed' the bearing blocks.

The air delivery system was unique- each block had a lengh of air line feeding it which was made from electrical wire insulation. Don't ask how I managed to strip 50 ft of insulation from the solid copper conductor- took a bit of time, but supplied me with air line with a very small inner diameter. That was enough to even out the airflow to each bearing block. If one lifted off slightly, it wouldn't bleed pressure from the others. One thing about using this method to restrict air flow- it's very consistent. I could have made up some adjustable valves and it would have worked also.

I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my pass​ion-

Comment

Wierd,
That's basically the same as what I linked to but yours is a complete bearing. I see no reason why not.

Years ago when I was maintaining some big laser cutting machines we used to have to strip the Y axis every 6 months because off the fumes off the cutting process, these ran on round supported rails and ball bushings.

The rails were cleaned with WD40 and the ball bushings were replaced. The local bearing company used to keep spares on the shelf to be called off as needed.

On one service they had forgotten to restock and no new ball bushings were available and the old ones were badly mauled. Frantic phone calls and all I could get were the teflon lined bushings, same dimensions and interchangeable, so fitted them to get the machine running and idea was to swap back to ball bushings next tine the rails got clogged up.

Never happened, they kept the rails clean and didn't deteriorate like the ball bushings. Finished up changing all the ball bushings on 5 machines to the teflon lined ones.

Comment

So if you were going to use air suspension anyway, wouldn't uhmw be just as good as teflon? The main difference would be that, without air, the uhmw is going to give some stick/slip. That's the conclusion I came to, and then I bought some snow sliders, which is some kind of slippery poly sheet. I've been using that ever since, even without air.

I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my pass​ion-